Seminars

Three-dimensional direct numerical simulation (DNS) with detailed chemical kinetics is used to investigate the stabilization of turbulent non-premixed flames in the wake of jet in cross-flow (JICF) configurations and the upstream propagation (flashback) of turbulent premixed flames in fully developed channel flow configurations. In the non-premixed case, results indicate that the core of the heat release is located near the trailing edge of the fuel jet, this representing the flame stabilization location at approximately 4 nozzle diameters away from the wall, and it is characterized by the simultaneous occurrence of locally stoichiometric reactants and low flow velocities in the mean. The response of flame stabilization to angle of injection and fuel composition is investigated; the DNS datasets indicate high sensitivity to the former and low to the latter. The DNS of premixed flames flashback (at ϕ = 0.55 and ϕ = 1.5) in the turbulent boundary layers of canonical fully-developed channel flows reveals the occurrence of near-wall flow reversal pockets immediately upstream of the flame surface regions that are convex towards the reactants. The flow reversals seem to originate in and migrate with the low velocity streaks of the turbulent boundary layer and are likely caused by and are proportional to the flame expansion ratio in a region of very low fluid velocity. Furthermore, they facilitate upstream flame propagation by creating a "flow blockage" ahead of the flame front that deflects the approaching flow away from the wall and towards the channel centerline, ultimately inducing flashback (front) velocities of approximately two times the laminar flame speed for all cases investigated."